Method for manufacturing separator web, method for manufacturing separator, separator web, and apparatus for manufacturing separator web

ABSTRACT

To easily specify the position of a defect in a separator, a method for producing a separator original sheet (12b) includes the steps of: forming a separator original sheet (12b) including a separator original sheet (12c) and a heat-resistant layer coated on the separator original sheet (12c); detecting a defect (D) in the separator original sheet (12b); and recording information including information on a position of the defect (D) which position is a position in the width direction of the separator original sheet (12b).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Section 371 of International Application No.PCT/JP2015/052749, filed Jan. 30, 2015, which was published in theJapanese language on Apr. 14, 2016 under International Publication No.WO 2016/056253 A1, and the disclosure of which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to (i) a method for producing a separatororiginal sheet for use in a lithium-ion secondary battery, (ii) a methodfor producing a separator, (iii) a separator original sheet, and (iv) aseparator original sheet producing apparatus.

BACKGROUND ART

There has been known a deficiency inspecting device for a sheet-shapedproduct including an optical film (Patent Literature 1). The deficiencyinspecting device receives information on a deficiency from a protectivefilm inspecting section, and forms a data code (for example, atwo-dimensional code or a QR Code [registered trademark]) having a fixedpitch and indicative of the deficiency. The deficiency inspecting deviceforms such a data code on a surface at an end of a PVA film originalsheet together with information on the position and productionidentification.

CITATION LIST Patent Literature

[Patent Literature 1] Japanese Patent Application Publication, Tokukai,No. 2008-116437 (Publication Date: May 22, 2008)

SUMMARY OF INVENTION Technical Problem

Production of a separator for use in a lithium-ion secondary battery,however, suffers from a defect in a separator original sheet. Enormousefforts are expended to specify the position of such a defect in aseparator original sheet.

It is an object of an embodiment of the present invention to provide amethod for producing a separator original sheet, a method for producinga separator, a separator original sheet, and a separator original sheetproducing apparatus each of which allows the position of a defect in aseparator original sheet to be easily specified.

Solution to Problem

In order to attain the above object, a separator original sheetproducing method in accordance with an embodiment of the presentinvention includes the steps of: forming a separator original sheet;detecting a defect in the separator original sheet; and recording defectinformation including information on a first position of the defectwhich first position is a position in a width direction of the separatororiginal sheet. The term “separator original sheet” refers to a wideseparator that has not been slit.

The above feature involves recording defect information includinginformation on a first position of the defect which first position is aposition in the width direction of the separator original sheet.Referring to information recorded as such makes it possible to easilyspecify the position of a defect in a separator original sheet. This inturn makes it possible to easily remove a defect in a separator originalsheet.

The separator original sheet producing method in accordance with anembodiment of the present invention may preferably be arranged such thatthe defect information further includes information on a second positionof the defect which second position is a position in a longitudinaldirection of the separator original sheet. The expression “longitudinaldirection of the separator original sheet” refers to the direction inwhich a workpiece is conveyed during a process of producing a separator.

The above arrangement makes it possible to, on the basis of theinformation on the second position, easily find the defect when theseparator original sheet is wound off.

The separator original sheet producing method in accordance with anembodiment of the present invention may preferably be arranged such thatthe defect information is recorded at a portion of the separatororiginal sheet which portion corresponds to a second position of thedefect which second position is a position in a longitudinal directionof the separator original sheet.

The above arrangement makes it possible to specify the second positionof a defect on the basis of the position at which defect information hasbeen recorded. Further, the defect information is recorded at a portionof the separator original sheet which portion corresponds to the secondposition of the defect. Thus, even in a case where the separatororiginal sheet has been stretched lengthwise, the lengthwise position ofthe defect is substantially not displaced from the lengthwise positionof the defect information. The lengthwise position of a defect is thuseasily specifiable even in the case where the separator original sheethas been stretched lengthwise.

In order to attain the above object, a separator producing method inaccordance with an embodiment of the present invention includes thesteps of: (a) forming a separator original sheet; (b) detecting a defectin the separator original sheet; (c) recording defect informationincluding information on a first position of the defect which firstposition is a position in a width direction of the separator originalsheet; (d) cutting the separator original sheet having the defect, ofwhich the information has been recorded in the step (c), in alongitudinal direction of the separator original sheet into a pluralityof separators; (e) reading the information; and (f) on a basis of theinformation read in the step (e), providing at least one of theplurality of separators with a mark for specifying the first position ofthe defect.

This feature involves providing, on the basis of the information read inthe step (e), at least one of the plurality of separators with a markfor specifying the position of the defect. This makes it possible toeasily remove a defective portion of a separator among the plurality ofseparators, prepared by slitting a separator original sheet, whichseparator has the defect.

The separator producing method in accordance with an embodiment of thepresent invention may preferably further include the steps of: (g)winding up the at least one of the plurality of separators, which atleast one of the plurality of separators has been provided with themark; (h) sensing the mark while carrying out an operation of windingoff the at least one of the plurality of separators, which has beenwound up in the step (g), and winding up the at least one of theplurality of separators again; and (i) in accordance with the sensing ofthe mark, stopping the operation and removing the defect.

The above arrangement, which involves removing a defect after theseparator is wound up, eliminates the need to stop the winding and thusimproves the working efficiency.

The separator producing method in accordance with an embodiment of thepresent invention may preferably be arranged such that in the step (i):the at least one of the plurality of separators is cut in the widthdirection at two positions opposite to each other in the longitudinaldirection with the defect therebetween; the defect is removed; and cutparts of the separator are then connected.

The above arrangement makes it possible to remove a defect in aseparator original sheet for separator production.

The separator producing method in accordance with an embodiment of thepresent invention may preferably be arranged such that in the step (c),the information is recorded at a widthwise end of the separator originalsheet.

The above arrangement makes it possible to recognize a defective portionby simply reading information recorded at a widthwise end of a separatororiginal sheet.

The separator producing method in accordance with an embodiment of thepresent invention may preferably be arranged such that in the step (c),the information is recorded in an information storing device.

The above arrangement makes it possible to recognize a defective portionby reading information recorded in an information storing device.

The separator producing method in accordance with an embodiment of thepresent invention may preferably be arranged such that the step (f) iscarried out by attaching a label.

In order to attain the above object, a separator original sheet inaccordance with an embodiment of the present invention includes: at awidthwise end thereof, information on a position of a defect in theseparator original sheet which position is a position in a widthdirection.

In order to attain the above object, a separator original sheetproducing apparatus in accordance with an embodiment of the presentinvention includes: a forming section configured to form a separatororiginal sheet; a defect detecting section configured to detect a defectin the separator original sheet; and a defect information recordingsection configured to record defect information including information ona position of the defect which position is a position in a widthdirection of the separator original sheet.

Advantageous Effects of Invention

An embodiment of the present invention produces the effect of providinga method for producing a separator original sheet, a method forproducing a separator, a separator original sheet, and a separatororiginal sheet producing apparatus each of which allows the position ofa defect in a separator to be easily specified.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating a cross-sectionalconfiguration of a lithium-ion secondary battery in accordance withEmbodiment 1.

FIG. 2 provides diagrams schematically illustrating details of theconfiguration of the lithium-ion secondary battery illustrated in FIG.1.

FIG. 3 provides diagrams schematically illustrating anotherconfiguration of the lithium-ion secondary battery illustrated in FIG.1.

FIG. 4 provides diagrams schematically illustrating a defect detectingstep and a defect information recording step both included in a methodfor marking a defect in a separator original sheet.

FIG. 5 provides diagrams illustrating a configuration of a base materialdefect inspecting device in the defect detecting step.

FIG. 6 provides diagrams illustrating a configuration of a coatingdefect inspecting device in the defect detecting step.

FIG. 7 provides diagrams illustrating a configuration of a pinholedefect inspecting device in the defect detecting step.

FIG. 8 provides diagrams schematically illustrating a configuration of aslitting apparatus configured to slit a separator.

FIG. 9 provides an enlarged view, a side view, and an elevational viewof a cutting device included in the slitting apparatus illustrated inFIG. 8.

FIG. 10 is a diagram schematically illustrating a reading step, a markproviding step, and a wind-up step all included in a method forspecifying the position of a defect in a separator.

FIG. 11 provides diagrams schematically illustrating a mark sensing stepand a defect removing step both included in a method for specifying theposition of a defect in a separator.

FIG. 12 provides diagrams schematically illustrating a defect detectingstep and a defect information recording step both included in a methodin accordance with Embodiment 2 for marking a defect in a separatororiginal sheet.

FIG. 13 is a diagram schematically illustrating a reading step, a markproviding step, and a wind-up step all included in a method forspecifying the position of a defect in a separator.

DESCRIPTION OF EMBODIMENTS

The following description will discuss embodiments of the presentinvention in detail.

Embodiment 1

The following description will discuss, in order, a lithium-ionsecondary battery, a separator, a heat-resistant separator, aheat-resistant separator producing method, a slitting apparatus, and acutting device each in accordance with Embodiment 1.

(Lithium-Ion Secondary Battery)

A nonaqueous electrolyte secondary battery, typically a lithium-ionsecondary battery, has a high energy density, and is therefore currentlywidely used not only as batteries for use in devices such as personalcomputers, mobile phones, and mobile information terminals, and for usein moving bodies such as automobiles and airplanes, but also asstationary batteries contributing to stable power supply.

FIG. 1 is a diagram schematically illustrating a cross-sectionalconfiguration of a lithium-ion secondary battery 1.

As illustrated in FIG. 1, the lithium-ion secondary battery 1 includes acathode 11, a separator 12, and an anode 13. Between the cathode 11 andthe anode 13, an external device 2 is connected outside the lithium-ionsecondary battery 1. While the lithium-ion secondary battery 1 is beingcharged, electrons move in a direction A. Meanwhile, while thelithium-ion secondary battery 1 is being discharged, electrons move in adirection B.

(Separator)

The separator 12 is provided so as to be sandwiched between the cathode11 (as a positive electrode) and the anode 13 (as a negative electrode)of the lithium-ion secondary battery 1. While separating the cathode 11and the anode 13, the separator 12 allows lithium ions to move betweenthe cathode 11 and the anode 13. The separator 12 contains, for example,a polyolefin (for example, polyethylene or polypropylene) as a materialthereof.

FIG. 2 provides diagrams schematically illustrating details of theconfiguration of the lithium-ion secondary battery 1 illustrated inFIG. 1. (a) of FIG. 2 illustrates a normal configuration. (b) of FIG. 2illustrates a state in which the temperature of the lithium-ionsecondary battery 1 has risen. (c) of FIG. 2 illustrates a state inwhich the temperature of the lithium-ion secondary battery 1 has sharplyrisen.

As illustrated in (a) of FIG. 2, the separator 12 is provided with manypores P. Normally, lithium ions 3 in the lithium-ion secondary battery 1can move back and forth through the pores P.

Note here that there may be, for example, a case where the lithium-ionsecondary battery 1 increases in temperature due to, for example, (i)overcharge of the lithium-ion secondary battery 1 or (ii) a largecurrent caused by a short circuit having occurred in an external device.In such cases, the separator 12 melts or softens, and the pores P areblocked as illustrated in (b) of FIG. 2. As a result, the separator 12shrinks. This stops the movement of the lithium ions 3, and consequentlystops the increase in temperature (described earlier).

Note, however, that the separator 12 suddenly shrinks in a case wherethe lithium-ion secondary battery 1 sharply increases in temperature. Inthis case, as illustrated in (c) of FIG. 2, the separator 12 may bebroken. Then, the lithium ions 3 leak out from the separator 12 whichhas been broken, so that the lithium ions 3 do not stop moving back andforth. Thus, the increase in temperature continues.

(Heat-Resistant Separator)

FIG. 3 provides diagrams schematically illustrating anotherconfiguration of the lithium-ion secondary battery 1 illustrated inFIG. 1. (a) of FIG. 3 illustrates a normal configuration, and (b) ofFIG. 3 illustrates a state in which the temperature of the lithium-ionsecondary battery 1 has sharply risen.

As illustrated in (a) of FIG. 3, the lithium-ion secondary battery 1 canfurther include a heat-resistant layer 4. The heat-resistant layer 4 andthe separator 12 form a heat-resistant separator 12 a (separator). Theheat-resistant layer 4 is laminated on one surface of the separator 12which surface is on the cathode 11 side. The heat-resistant layer 4 mayalternatively be laminated on (i) a surface of the separator 12 whichsurface is on the anode 13 side or on (ii) both surfaces of theseparator 12. Further, the heat-resistant layer 4 is provided with poresthat are similar to the pores P. Normally, lithium ions 3 move back andforth through the pores P and the pores of the heat-resistant layer 4.The heat-resistant layer 4 contains, for example, wholly aromaticpolyamide (aramid resin) as a material thereof.

As illustrated in (b) of FIG. 3, even in a case where the temperature ofthe lithium-ion secondary battery 1 has sharply risen and accordinglythe separator 12 has melted or softened, the shape of the separator 12is maintained because the heat-resistant layer 4 supports the separator12. Thus, such a sharp increase in temperature merely results in meltingor softening of the separator 12 and consequent blocking of the pores P.This stops the movement of the lithium ions 3, and consequently stopsoverdischarge and overcharge (described earlier). The separator 12 isthus prevented from being broken.

(Steps of Producing Heat-Resistant Separator Original Sheet (SeparatorOriginal Sheet))

How to produce the heat-resistant separator 12 a of the lithium-ionsecondary battery 1 is not particularly limited. The heat-resistantseparator 12 a can be produced by a publicly known method. The followingdiscussion assumes a case where the separator 12 contains polyethyleneas a main material. However, even in a case where the separator 12contains another material, the similar steps can still be applied toproduction of the separator 12.

For example, it is possible to employ a method including the steps offirst forming a film by adding a plasticizer to a thermoplastic resin,and then removing the plasticizer with use of an appropriate solvent.For example, in a case where the separator 12 is made of a polyethyleneresin containing an ultrahigh molecular weight polyethylene, it ispossible to produce a separator 12 by the following method.

This method includes (1) a kneading step of obtaining a polyethyleneresin composition by kneading an ultrahigh molecular weight polyethyleneand an inorganic filler such as calcium carbonate, (2) a rolling step offorming a film from the polyethylene resin composition, (3) a removalstep of removing the inorganic filler from the film obtained in the step(2), and (4) a stretching step of obtaining a separator 12 by stretchingthe film obtained in the step (3).

In the removal step, many fine pores are provided in the film. The finepores of the film stretched in the stretching step become theabove-described pores P. The separator 12 formed as a result is apolyethylene microporous film having a prescribed thickness and aprescribed air permeability.

Note that the kneading step may involve kneading (i) 100 parts by weightof the ultrahigh molecular weight polyethylene, (ii) 5 parts by weightto 200 parts by weight of a low-molecular weight polyolefin having aweight-average molecular weight of 10000 or less, and (iii) 100 parts byweight to 400 parts by weight of the inorganic filler.

Thereafter, in a coating step, the heat-resistant layer 4 is formed on asurface of the separator 12. For example, on the separator 12, anaramid/NMP (N-methylpyrrolidone) solution (coating solution) is applied,and thereby, the heat-resistant layer 4 that is an aramid heat-resistantlayer is formed. The heat-resistant layer 4 can be provided on only onesurface or both surfaces of the separator 12. Alternatively, theheat-resistant layer 4 can be formed by using alumina/carboxymethylcellulose for coating.

The method for coating the separator 12 with a coating solution is notparticularly limited as long as uniform wet coating can be performed bythe method. The method can be a conventionally publicly known methodsuch as a capillary coating method, a spin coating method, a slit diecoating method, a spray coating method, a dip coating method, a rollcoating method, a screen printing method, a flexo printing method, a barcoater method, a gravure coater method, or a die coater method. Theheat-resistant layer 4 has a thickness which can be controlled byadjusting (i) the thickness of a coating wet film, (ii) thesolid-content concentration (which is the sum of concentrations of abinder and a filler in the coating solution), and/or (iii) the ratio ofthe filler to the binder.

It is possible to use a resin film, a metal belt, a drum or the like asa support with which the separator 12 is fixed or transferred incoating.

This operation allows for production of a heat-resistant separatororiginal sheet 12 b which is a separator original sheet 12 c on whichthe heat-resistant layer 4 is laminated (forming step) (see FIG. 4). Theheat-resistant separator original sheet 12 b thus produced is woundaround a core 53 having a cylindrical shape (see FIG. 4). Note that thesubject to be produced by the above production method is not limited tothe heat-resistant separator original sheet 12 b. The above productionmethod does not necessarily include the coating step. In this case, thesubject to be produced is a separator original sheet 12 c.

In a case where during production of a heat-resistant separator for usein a lithium-ion secondary battery, an inspecting device has detected adefect in a coating step of preparing a heat-resistant separatororiginal sheet including a separator original sheet coated with aheat-resistant layer, the original sheet having the defect is providedwith a line drawn with a marker before the heat-resistant separatororiginal sheet is wound up. In the subsequent slitting step, theheat-resistant separator original sheet is wound off. Then, when anoperator sees the line drawn with the marker on the heat-resistantseparator original sheet wound off, the operator stops the operation ofwinding off the heat-resistant separator original sheet. Next, theoperator visually checks the position, along the width of theheat-resistant separator original sheet, of the defect indicated by theline drawn with the marker. Next, that portion of the heat-resistantseparator original sheet on which the line is drawn with the marker iscut by a cutting device lengthwise to form a plurality of heat-resistantseparators. Then, the operator attaches, to one of the heat-resistantseparators, a piece of tape in such a manner that (i) the tape coincideswith the lengthwise position on the heat-resistant separator at whichposition the defect indicated by the line drawn with the marker ispresent and that (ii) the tape extends beyond a side of theheat-resistant separator. The heat-resistant separator, to which thetape is attached in such a manner that the tape extends beyond a side ofthe heat-resistant separator, is wound up around a wind-up roller.

Next, the heat-resistant separator wound up around the wind-up roller iswound off from the wind-up roller and then wound up around an additionalwind-up roller in an additional wind-up step. When an operator sees thetape in the additional wind-up step, the operator stops the operation ofthe additional wind-up step. The operator then cuts off, in the widthdirection, that portion of the heat-resistant separator at which thedefect indicated by the tape is present, and removes that portion fromthe rest. Next, the heat-resistant separator on the side of the wind-uproller is connected with the heat-resistant separator on the side of theadditional wind-up roller. Then, the operation of the additional wind-upstep is resumed, so that the heat-resistant separator is all wound offfrom the wind-up roller and then wound up around the additional wind-uproller.

This procedure is, however, problematic in that it merely involvesdrawing a line on a heat-resistant separator original sheet with amarker in a case where an inspecting device has detected a defect in theheat-resistant separator original sheet. Thus, when an operator sees theline in the subsequent slitting step, the operator needs to stop theoperation of winding off the heat-resistant separator original sheet andvisually check the widthwise position of the defect. Enormous effortsare thus needed in order to specify the position of the defect in aplurality of heat-resistant separators prepared by slitting theheat-resistant separator original sheet.

FIG. 4 provides diagrams schematically illustrating a defect detectingstep and a defect information recording step both included in a methodfor marking a defect in the heat-resistant separator original sheet 12b. (a) of FIG. 4 is an elevational view of the two steps, whereas (b) ofFIG. 4 is a plan view of the two steps. FIG. 5 provides diagramsillustrating a configuration of a base material defect inspecting device55 in the defect detecting step. FIG. 6 provides diagrams illustrating aconfiguration of a coating defect inspecting device 57 in the defectdetecting step. FIG. 7 provides diagrams illustrating a configuration ofa pinhole defect inspecting device 58 in the defect detecting step.

A heat-resistant layer is formed on a separator original sheet 12 c bythe coating section 54 so that a heat-resistant separator original sheet12 b is prepared. The heat-resistant separator original sheet 12 b iswound up around a core 53. Specifically, a base material inspecting step(defect detecting step) is a step of inspecting the separator originalsheet 12 c for a defect D. The base material inspecting step is carriedout by a base material defect inspecting device 55 (defect detectingsection, separator original sheet producing apparatus) between a step ofunreeling the separator original sheet 12 c and the coating step. Thebase material defect inspecting device 55 includes a light source 55 aand a detector 55 b that are so positioned as to sandwich the separatororiginal sheet 12 c. The light source 55 a emits light in a directionperpendicular to the front and back surfaces of the separator originalsheet 12 c, whereas the detector 55 b detects light having passedthrough the separator original sheet 12 c. This allows the base materialdefect inspecting device 55 to inspect the separator original sheet 12 cfor a defect D present therein (defect detecting step). The defect Dpresent in the separator original sheet 12 c is, for example, a throughhole (pinhole), an inappropriate film thickness, or a defect caused by aforeign substance.

A coating inspecting step (defect detecting step) is a step ofinspecting the heat-resistant layer 4, formed on the separator originalsheet 12 c, for a defect D. The coating inspecting step is carried outby a coating defect inspecting device 57 (defect detecting section,separator original sheet producing apparatus) between the coating stepand a step of winding up the heat-resistant separator original sheet 12b around the core 53. The coating defect inspecting device 57 includes alight source 57 a and a detector 57 b that are positioned on the side ofthe heat-resistant layer 4 of the heat-resistant separator originalsheet 12 b. The light source 57 a emits light to the heat-resistantlayer 4, whereas the detector 57 b detects light having been reflectedby the heat-resistant layer 4. This allows the coating defect inspectingdevice 57 to detect a defect D present in the heat-resistant layer 4.The defect D present in the heat-resistant layer 4 is, for example, acrease, peeling off, repellency, and a surface failure. The repellencyrefers to a defect of a foreign substance, oil, or the like on thesurface of the separator original sheet 12 c repelling the coatingsolution from the surface, with the result of local absence of aheat-resistant layer 4 or local formation of an extremely thinheat-resistant layer 4. The surface failure refers to a failure in thethickness of the heat-resistant layer 4.

A pinhole inspecting step (defect detecting step) is a step ofinspecting the heat-resistant separator original sheet 12 b for a defectD in the form of a pinhole. The pinhole inspecting step is carried outby a pinhole defect inspecting device 58 (defect detecting section,separator original sheet producing apparatus) positioned between thecoating defect inspecting device 57 and a defect information recordingdevice 56 (defect information recording section, separator originalsheet producing apparatus). The pinhole defect inspecting device 58includes a light source 58 a, a detector 58 b, and a slit 58 c. Thelight source 58 a is positioned on the side of the separator originalsheet 12 c of the heat-resistant separator original sheet 12 b, andemits light in a direction perpendicular to the front and back surfacesof the heat-resistant separator original sheet 12 b. The slit 58 c letsthe light pass therethrough and travel toward the heat-resistantseparator original sheet 12 b. The detector 58 b detects a defect D onthe basis of light having passed through the heat-resistant separatororiginal sheet 12 b. The defect D in the form of a pinhole has adiameter ranging from several hundreds of micrometers to severalmillimeters.

The production process involves a defect information recording device 56positioned between the pinhole defect inspecting device 58 and the core53. The defect information recording device 56 records, on theheat-resistant separator original sheet 12 b, a defect code DC (defectinformation) indicative of information on the position of any defect Ddetected by the base material defect inspecting device 55, the coatingdefect inspecting device 57, or the pinhole defect inspecting device 58.The defect information recording device 56 records such a defect code DCat a portion on a widthwise side of the heat-resistant separatororiginal sheet 12 b which portion corresponds to the lengthwise positionof the defect D on the heat-resistant separator original sheet 12 b. Thedefect code DC may be code data such as a two-dimensional code or QRCode (registered trademark). The information on the position indicateswhere the defect D is positioned in the longitudinal and widthdirections of the heat-resistant separator original sheet 12 b. Theinformation on the position may include information with which the typeof the defect D is distinguishable. The type of a defect D is, forexample, (i) a structural defect in the base material for which defectthe base material defect inspecting device 55 inspects the separatororiginal sheet 12 c, (ii) a defect caused in the applying step for whichdefect the coating defect inspecting device 57 inspects theheat-resistant layer 4, or (iii) a defect in the form of an opening forwhich defect the pinhole defect inspecting device 58 inspects theheat-resistant separator original sheet 12 b.

The separator original sheet 12 c or heat-resistant separator originalsheet 12 b is subjected to a film tension of typically not more than 200N/m, preferably not more than 120 N/m. The term “film tension” refers toa tension applied to a film being conveyed, the tension being applied inthe conveying direction over a unit widthwise length of the film. Forinstance, with a film tension of 200 N/m, a force of 200 N is applied tothe film over a width of 1 m. A film tension of more than 200 N/m mayform a wrinkle in the conveying direction of the film and decrease theaccuracy of defect inspection. The film tension is typically not lessthan 10 N/m, preferably not less than 30 N/m. A film tension of lessthan 10 N/m may cause slack in the film or let the film meander. Theseparator original sheet 12 c or heat-resistant separator original sheet12 b has pores P, and is subjected to a film tension lower than a filmtension applied to a non-porous film such as an optical film. Theseparator original sheet 12 c or heat-resistant separator original sheet12 b thus has a physical property of being stretchable more easily thana non-porous film such as an optical film. As such, in a case where adefect code DC is recorded at a portion on a widthwise side of theheat-resistant separator original sheet 12 b which portion correspondsto the lengthwise position of the defect D on the heat-resistantseparator original sheet 12 b, the lengthwise position of the defect Dis substantially not displaced from the lengthwise position of thedefect code DC even in a case where the heat-resistant separatororiginal sheet 12 b has been stretched lengthwise. The lengthwiseposition of a defect D is thus easily specifiable even in the case wherethe heat-resistant separator original sheet 12 b has been stretchedlengthwise.

The heat-resistant separator original sheet 12 b with a defect code DCrecorded at a portion on a widthwise side thereof is wound up around thecore 53. The core 53, around which the heat-resistant separator originalsheet 12 b has been wound up, is carried to a position for thesubsequent slitting step.

(Slitting Apparatus)

The heat-resistant separator 12 a, produced from the heat-resistantseparator original sheet 12 b (hereinafter referred to as “separatororiginal sheet”), or the separator 12 (hereinafter referred to as“separator”), produced from the separator original sheet 12 c,preferably has a width (hereinafter referred to as “product width”)suitable for application products such as the lithium-ion secondarybattery 1. For improved productivity, however, the separator originalsheet is produced so as to have a width that is equal to or larger thana product width. Then, after having been once produced so as to have awidth equal to or larger than the product width, the separator originalsheet is cut (slit) into a separator(s) having the product width. Notethat the expression “width of a/the separator” means a dimension of theseparator in a direction that is parallel to a plane in which theseparator extends and that is perpendicular to the longitudinaldirection of the separator.

FIG. 8 provides diagrams schematically illustrating a configuration of aslitting apparatus 6 configured to slit the separator original sheet 12b. (a) of FIG. 8 illustrates the entire configuration, and (b) of FIG. 8illustrates an arrangement before and after slitting the separatororiginal sheet 12 b.

As illustrated in (a) of FIG. 8, the slitting apparatus 6 includes arotatably supported cylindrical wind-off roller 61, rollers 62 to 65,and wind-up rollers 69. The slitting apparatus 6 is further providedwith a cutting device 7 (see FIG. 9) described later.

(Before Slitting)

In the slitting apparatus 6, a cylindrical core 53 on which theseparator original sheet 12 b is wrapped is fit on the wind-off roller61. As illustrated in (a) of FIG. 8, the separator original sheet 12 bis wound off from the core 53 to a route U or L. The separator originalsheet 12 b thus wound off is conveyed to the roller 64 via the roller 63at a speed of, for example, 100 m/min. In the conveying step, theseparator original sheet 12 b is slit lengthwise into a plurality ofseparators 12 a.

(After Slitting)

As illustrated in (a) of FIG. 8, one or more of the plurality ofseparators 12 a are wound up around respective cores 81 fit on theplurality of wind-up rollers 69. Further, another one or more of theplurality of separators 12 a are wound up around respective cores 81 fiton the plurality of wind-up rollers 69. Note that each of the slitseparators wound into a roll form is referred to as a “separator roll”.

(Cutting Device)

FIG. 9 provides views each illustrating a configuration of the cuttingdevice 7 of the slitting apparatus 6 illustrated in (a) of FIG. 8. (a)of FIG. 9 is a side view of the cutting device 7, and (b) of FIG. 9 is afront view of the cutting device 7.

As illustrated in (a) and (b) of FIG. 9, the cutting device 7 includes aholder 71 and a blade 72. The holder 71 is fixed to a housing or thelike provided in the slitting apparatus 6. The holder 71 holds the blade72 in such a manner that the blade 72 and the separator original sheet12 b being conveyed have a fixed positional relation. The blade 72 has afinely sharpened edge and slits the separator original sheet by usingthis edge.

FIG. 10 is a diagram schematically illustrating a reading step, a markproviding step, and a wind-up step all included in a method forspecifying the position of a defect in a separator 12 a. The separatororiginal sheet 12 b is wound off from the core 53 (see FIG. 8) at afixed speed (for example, 80 m/min). A reading section 73 reads a defectcode DC recorded at a portion on a widthwise side of the separatororiginal sheet 12 b (reading step). The plurality of cutting devices 7,included in the slitting apparatus 6, cut the separator original sheet12 b lengthwise to prepare a plurality of separators 12 a (cuttingstep).

Next, a mark providing device 74 identifies one of the plurality ofseparators 12 a, prepared by the plurality of cutting devices 7, on thebasis of information on the widthwise position of a defect D whichinformation is in the form of a defect code DC and has been read by thereading section 73. The mark providing device 74 then provides a mark Lat a position corresponding to the defect D in the separator 12 aidentified as above (mark providing step). In a case where there are aplurality of defects D present, the mark providing device 74 identifiesa plurality of separators 12 a. The mark L is preferably a label, so themark providing device 74 is preferably a labeler.

The mark L may be, instead of a label, a mark drawn with a pen or a markapplied by an injector. The mark L may also be a thermolabel, which isprinted by heating the separator 12 a (made of resin). The mark L mayalso be provided by forming a hole in the separator 12 a with use of alaser.

The plurality of separators 12 a, prepared by cutting the separatororiginal sheet 12 b with use of the cutting devices 7, are each wound uparound one of a plurality of cores 81 (wind-up step).

The mark providing device 74 then records information on the position ofthe defect D in the lengthwise direction of the separator original sheet12 b, which defect D is indicated by a defect code DC. The markproviding device 74 records such information as a defect code DC2 on (i)an outermost portion 86 of the separator 12 a identified and wound upand/or (ii) the core 81.

FIG. 11 provides diagrams schematically illustrating a mark sensing stepand a defect removing step both included in a method for specifying theposition of a defect in a separator 12 a. (a) of FIG. 11 is a diagramschematically illustrating the mark sensing step. (b) of FIG. 11 is adiagram schematically illustrating the defect removing step. First, amark sensing device 83 reads a defect code DC2 recorded on the outermostportion 86 and/or core 81. The mark providing device 74 receivesinformation read by the mark sensing device 83 and attaches a mark L tothe separator 12 a with the defect D present therein. The mark sensingstep then starts an operation of winding off the separator 12 a from thecore 81 and winding up the heat-resistant separator 12 a again around acore 82. Next, the mark sensing device 83, on the basis of informationon the position of the defect D (indicated by the defect code DC2 readby the mark sensing device 83) in the lengthwise direction of theseparator original sheet 12 b, slows the above operation when the defectD has become close to the core 82.

The mark sensing device 83 then senses the mark L, which is attached tothe position corresponding to the defect D in the separator 12 a (marksensing step). When the mark sensing device 83 has sensed the mark L,the mark sensing device 83 stops the operation of winding up theseparator 12 a again. Then, a defect removing device 84 cuts theseparator 12 a widthwise at (i) a position upstream of the defect D(which corresponds to the mark L) and (ii) a position downstream of thedefect D, and removes the defect D from the separator 12 a (defectremoving step). The defect removing step may alternatively be carriedout manually by an operator instead of the defect removing device 84.Then, a connecting device 85 connects two portions of the separator 12 athat are separated from each other as the result of cutting theseparator 12 a (connecting step). The connecting step may alternativelybe carried out manually by an operator instead of the connecting device85. Next, the connecting device 85 resumes the operation of winding upthe separator 12 a again. The operation of winding off the separator 12a from the core 81 and winding up the separator 12 a again around thecore 82 is then completed. The two portions of the separator 12 a, whichresult from dividing the separator 12 a, may alternatively be leftunconnected to be individually wound up around separate cores. In otherwords, the separator 12 a may be wound up again in such a manner thatthat portion of the separator 12 a which is downstream of the removedportion is wound up around the core 82, whereas that portion of theseparator 12 a which is upstream of the removed portion is wound uparound another core.

Embodiment 2

Embodiment 1 is an example in which information on the position of adefect D present in a separator original sheet 12 b is recorded at awidthwise end of the separator original sheet 12 b. The presentinvention is, however, not limited to such a configuration, and may beconfigured such that information on the position of a defect D isrecorded in an information storing device.

FIG. 12 provides diagrams schematically illustrating a defect detectingstep and a defect information recording step both included in a methodin accordance with Embodiment 2 for marking a defect in a separatororiginal sheet 12 b. FIG. 13 is a diagram schematically illustrating areading step, a mark attaching step, and a wind-up step all included ina method for specifying the position of a defect in a separator 12 a.Any constituent element of Embodiment 2 that is identical to acorresponding constituent element described earlier for Embodiment 1 isassigned a common reference sign, and is not described in detail here.

A defect information recording device 56 a (defect information recordingsection, separator original sheet producing apparatus) records, in aninformation storing device 91, positional information indicative of thelengthwise and widthwise positions of a defect D that is present in theseparator original sheet 12 c or 12 b and that has been detected by thebase material defect inspecting device 55, the coating defect inspectingdevice 57, or the pinhole defect inspecting device 58. A reading section73 a reads the positional information from the information storingdevice 91 (reading step).

The present invention is not limited to the embodiments, but can bealtered by a skilled person in the art within the scope of the claims.Any embodiment derived from a proper combination of technical means eachdisclosed in a different embodiment is also encompassed in the technicalscope of the present invention.

INDUSTRIAL APPLICABILITY

An embodiment of the present invention is applicable to (i) a method formarking a defect in a separator original sheet for use in a lithium-ionsecondary battery, (ii) a method for specifying the position of a defectin a separator, (iii) a separator original sheet, and (iv) a separatororiginal sheet producing apparatus.

REFERENCE SIGNS LIST

-   -   4 Heat-resistant layer    -   6 Slitting apparatus    -   7 Cutting device (cutting machine)    -   12 Separator    -   12 a Heat-resistant separator (separator)    -   12 b Heat-resistant separator original sheet (separator original        sheet)    -   12 c Separator original sheet    -   54 Coating section (separator original sheet producing        apparatus)    -   55 Base material defect inspecting device (defect detecting        section, separator original sheet producing apparatus)    -   57 Coating defect inspecting device (defect detecting section,        separator original sheet producing apparatus)    -   58 Pinhole defect inspecting device (defect detecting section,        separator original sheet producing apparatus)    -   56, 56 a Defect information recording device (defect information        recording section, separator original sheet producing apparatus)    -   73 Reading section    -   74 Mark providing device    -   81 Core    -   82 Core    -   83 Mark sensing device    -   84 Defect removing device    -   85 Connecting device    -   86 Outermost portion    -   91 Information storing device    -   D Defect    -   DC, DC2 Defect code (positional information)    -   L Mark

The invention claimed is:
 1. A separator original sheet producingmethod, comprising the steps of: forming a porous separator originalsheet for a battery; detecting a defect in the separator original sheet;and forming a defect code including information on a first position ofthe defect which first position is a position in a width direction ofthe separator original sheet, the defect code being formed at a portionof the separator original sheet which portion corresponds to a secondposition of the defect which second position is a position in alongitudinal direction of the separator original sheet, so that theportion at which the defect code is formed indicates the second positionof the defect, wherein the separator original sheet includes a basematerial and a heat-resistant layer laminated on the base material,wherein the defect includes at least one of a base material defectpresent in the base material and a heat-resistant layer defect presentin the heat-resistant layer, and wherein the defect code includesinformation for distinguishing between the base material defect and theheat-resistant layer defect.
 2. A separator producing method, comprisingthe steps of: (a) forming a separator original sheet for a battery, theseparator original sheet being porous; (b) detecting a defect in theseparator original sheet; (c) forming a defect code includinginformation on a first position of the defect which first position is aposition in a width direction of the separator original sheet, thedefect code being formed at a portion of the separator original sheetwhich portion corresponds to a second position of the defect whichsecond position is a position in a longitudinal direction of theseparator original sheet, so that a portion at which the defect code isformed indicates the second position of the defect; (d) cutting theseparator original sheet having the defect, of which the information hasbeen recorded in the step (c), in a longitudinal direction of theseparator original sheet into a plurality of separators; (e) reading theinformation; and (f) on a basis of the information read in the step (e),identifying at least one of a plurality of separators and providing theat least one of the plurality of separators with a mark for specifyingthe first position of the defect, the mark being provided at a positionof the at least one of the plurality of separators which corresponds tothe defect.
 3. The separator producing method according to claim 2,further comprising the steps of: (g) winding up the at least one of theplurality of separators, which at least one of the plurality ofseparators has been provided with the mark; (h) sensing the mark whilecarrying out an operation of winding off the at least one of theplurality of separators, which has been wound up in the step (g), andwinding up the at least one of the plurality of separators again; and(i) in accordance with the sensing of the mark, stopping the operationand removing the defect.
 4. The separator producing method according toclaim 3, wherein in the step (i): the at least one of the plurality ofseparators is cut in the width direction at two positions opposite toeach other in the longitudinal direction with the defect therebetween;the defect is removed; and cut parts of the separator are thenconnected.
 5. The separator producing method according to claim 2,wherein in the step (c), the defect code is recorded at a widthwise endof the separator original sheet.
 6. The separator producing methodaccording to claim 2, wherein the step (f) is carried out by attaching alabel.
 7. A porous separator original sheet for a battery, comprising, adefect code including information on a first position of a defect in theseparator original sheet which first position is a position in a widthdirection, the defect code being formed at a portion of a widthwise endof the separator original sheet which portion corresponds to a secondposition of the defect which second position is a position in alongitudinal direction, so that the portion at which the defect code isformed indicates the second position of the defect, wherein theseparator original sheet includes a base material and a heat-resistantlayer laminated on the base material, wherein the defect includes atleast one of a base material defect present in the base material and aheat-resistant layer defect present in the heat-resistant layer, andwherein the defect code includes information for distinguishing betweenthe base material defect and the heat-resistant layer defect.
 8. Aseparator original sheet producing apparatus, comprising: a formingsection configured to form a porous separator original sheet for abattery; a defect detecting section configured to detect a defect in theseparator original sheet; and a defect information recording sectionconfigured to form a defect code including information on a position ofthe defect which position is a position in a width direction of theseparator original sheet, the defect code being formed at a portion ofthe separator original sheet which portion corresponds to a secondposition of the defect which second position is a position in alongitudinal direction of the separator original sheet, so that theportion at which the defect code is formed indicates the second positionof the defect, wherein the separator original sheet includes a basematerial and a heat-resistant layer laminated on the base material,wherein the defect includes at least one of a base material defectpresent in the base material and a heat-resistant layer defect presentin the heat-resistant layer, and wherein the defect code includesinformation for distinguishing between the base material defect and theheat-resistant layer defect.